Apparatus for enlarging an extremity of a plastic pipe

ABSTRACT

This invention is directed to apparatus for enlarging or belling an extremity of a plastic pipe so that the extremity of an adjacent length of pipe may be received and retained therein. An expanding mandrel is provided, and this mandrel includes expander jaws, expander wedges, and expander wedge guides which engage a tapered spindle. A continuous steel sheath surrounds the mandrel components and longitudinal movement of the tapered spindle provides progressive enlargement or reduction of the mandrel diameter.

D United States Patent 1 3,677,684 Platz [451 July 18, 1972 [541 APPARATUS FOR ENLARGING AN 3,248,756 5/1966 Mills et a1. ..18/l9 TE EXTRENIITY OF A PLASTIC PIPE 729,099 5/1903 Smith ....18/l9 TE UX 2,943,667 7/1960 Ewing et 81.. ..18/4$ R UX 1 1 lnvemofl Gerald Plm, Champwsn, 3,373,460 3/1968 Ladney, Jr... .249/152 x [73] Assignee: National Distillers and Chemical corpora. 1,698,999 1/1929 Hothersall.... ...18/ 19 TB UX on, New York, N Y 1,625,131 4/1927 M11181 18/D1G. 5 1,705,843 3/1929 Walter ..72/392 [22] Filed: Dec. 15, 1969 Primary Examiner-J. Howard Flint, Jr. [2]] Appl' 884301 Attamey-Allen A. Meyer, Jr.

[52] US. Cl ..42$/393, 425/469 [57] ABSTRACT 32 5' This invention is directed to apparatus for enlarging or belling l 8 45 393 an extremity of a plastic pipe so that the extremity of an ad- 249 78480 1 g 2 I 3 3 5 K 28 jacent length of pipe may be received and retained therein. An expanding mandrel is provided, and this mandrel includes expander jaws, expander wedges, and expander wedge guides [56] References Cited which engage a tapered spindle. A continuous steel sheath sur- UNITED STATES PATENTS rounds the mandrel components and longitudinal movement of the tapered spindle provides progressive enlargement or 3,339,242 9/1967 Lamb ..l8/45 R X reduction f h mandrel diameten 2,672,175 3/1954 Howard ..18/19 TE UX 2,948,031 8/1960 Webb ..18/D1G. 5 6 Claim, 12 Drawing Figures 3 13 13a 23b 20 24 n 17d 1 w 16 2 3 230. i 21 11o. j 1;; 1 1e v fl i f 16a 1 I I A f 1 j w de 1.. l mu 2 23 23a "-'k' 14 f 3 l|e 17 l (IO Patented July 18, 1972 FIG.|

5 Sheets-Sheet 1 INVENTOR G E RA LD M P L ATZ ATTORNEY INVENTOR TTORNE Patented July 18, 1972 5 Sheets-Sheet 2 z M/ T ,l A l D. mm mm w G A R m Ir E G 9 9 Y 9 Patented July 18, 1972 v 5 Sheets-Sheet 5 INVENTOR GERAL'D M. PLATZ ATTORNEY Patented July 18, 1972 3,677,684

5 Sheets-Sheet 4 FIG.5

24 n l7d 25 INVENTOR GERALD M. PLATZ BY W,

ATTORNEY Patented July 18, 1972 3,677,684

5 Sheets-Sheet 5 ATTORYE'Y APPARATUS FOR ENLARGING AN EXTREMITY OF A PLASTIC PIPE This invention relates to apparatus for expanding or enlarging an extremity of a length of flexible tubing or pipe to permit the ready assembly of an adjacent length of such tubing or pipe. The piping or tubing with which we here are concerned may be produced by extrusion or related processes from such polyolefins as polyethylene, polypropylene, polybutene, and the like, and are well known in this art.

Difficulties have been experienced in connection with the joining together of adjacent lengths of such pipe or tubing and prior art practices which include the use of fusing operations, solvents, and adhesives, have proven unsatisfactory. One particularly efficient method for accomplishing the results desired is through the enlargement, as by a belling operation, of one extremity of a pipe length to an internal diameter complementary to the external diameter of the adjacent pipe length, which then may be received telescopically within said enlarged extremity.

Accordingly, it is a major object of the present invention to provide novel apparatus for the ready expansion or enlarge ment of an extremity of a flexible pipe produced from plastic material whereby the extremity of an adjacent pipe length may be received and retained therein with particular convenience.

It is a further object of the invention to provide a device of the class set forth which may be utilized with pipe lengths of varying interior diameters and will be adjustable from an inoperative to an operative position, to fit within a pipe length and then be expanded to enlarge the extremity of said pipe length to the diameter or extent required.

It is still a further object of the present invention to provide a novel method for joining adjacent lengths of flexible plastic pipe by enlarging or belling an extremity of one length of such pipe to an interior diameter complementary to the exterior diameter of the next adjacent length of pipe which then may be received and securely retained within said enlarged extremity.

Briefly stated, the invention comprises the utilization of an expanding mandrel including a plurality of jaws or segments which are slidably associated with a conical spindle, these jaws being surrounded by an encompassing spring steel sheath to provide a smooth peripheral surface. Lateral movement of the spindle in one direction with respect to the jaws will result in the opening of the jaws from a retracted to an operative position, thereby increasing the diameter of the spring steel sheath and enlarging the interior diameter of the extremity of a length of plastic pipe within which the mandrel has been positioned. It will be understood that the gap between adjacent segments or jaws will be increased in direct relationship to the extent of movement of the segments upon the spindle, and is a function of the number of jaws and/or the expansion ratio. However, these gaps are bridged by the spring steel sheath which increases in diameter as the jaws open and, at all times, provides a smooth and continuous peripheral surface which contacts the interior surface of the plastic pipe being enlarged.

Further objects and advantages of the invention will be readily apparent from the accompanying drawings and following description wherein:

FIG. 1 is a side elevational view of a novel pipe enlarging or expanding tool or apparatus constructed in accordance with the present invention;

FIG. 2 is a longitudinal sectional view, on an enlarged scale, taken on the line 2-2 of FIG. 3 through the novel expanding mandrel, parts being broken away, the adjustable jaws being in expanded or operative position;

FIG. 3 is a transverse sectional view through the expanding mandrel, taken on the line 33 of FIG. 1 and also illustrating the jaws in expanded position;

FIG. 4 is a transverse sectional view through the expanding mandrel, similar to FIG. 3 and illustrating the jaws in fully retracted position;

FIG. 5 is a side elevational view of the expanding mandrel and spindle in retracted or inoperative position illustrating, in section, the extremity of a length of plastic pipe positioned thereupon;

FIG. 6 is a side elevational view, similar to FIG. 6, and illustrating the spindle in operative position with the expanding mandrel enlarged and the interior diameter of the length of plastic pipe having been increased so as to be complementary to the exterior diameter of the adjacent pipe length to be connected thereto;

FIG. 7 is a side elevational view of the operative spindle per se;

FIG. 8 is a transverse sectional view through the expanding mandrel taken on the line 8-8 of H16. 2 and looking in the direction of the arrows;

FIG. 9 is a detail sectional view taken on the line 9--9 of FIG. 8;

FIG. 10 is a perspective view of an; expanding guide which provides operative association between each expanding wedge of the mandrel and the spindle;

FIG. 11 is a perspective view of the preferred form of expander wedge employed; and

FIG. 12 is a perspective view of one of the expander jaws.

As shown in the drawings, the novel apparatus of the present invention includes a stand or base portion 10 including a vertically disposed mounting plate 11, secured to standards or the like 12, a spindle supporting U-shaped bracket 13 being attached to one face of the mounting plate by any suitable means such as bolts or the like 13a.

An internally threaded adjusting element or hand wheel 14 having a hub portion 14a is rotatably received within a suitable aperture in the bracket 13 and a longitudinally disposed threaded adjusting rod 15 extends through said handwheel and projects through the mounting plate 11 which carries a tubular guide 11a through which the adjusting rod 15 passes. A conical and outwardly tapered spindle or expander 16 is mounted upon the reduced extremity 15a of the adjusting rod 15, the peripheral surface.of said spindle being provided with a plurality of uniformly spaced expander guide receiving slots 16a or cam surfaces (six such slots being illustrated) for a purpose to be described more fully hereafter. It will obvious that rotation of the handwheel 14 in one direction (clockwise) will advance the adjusting rod 15 and the spindle or expander 16 in a direction away from the mounting plate 11 and that rotation of the handwheel in the opposite direction (counterclockwise) will move the adjusting rod and the spindle toward the mounting plate 11.

The novel expanding mandrel of the present invention, as shown more particularly in FIGS. 2 through 6 of the drawings, is constituted by a plurality of expander jaws 17 and a similar number of expander wedges 18, each of said expander wedges being mounted upon the outer extremity of an expander wedge guide 19, the inner extremity of each wedge guide being received within a slot 16a provided in the peripheral surface of the spindle 16. These slots are uniformly spaced and provide an assembled relationship whereby the expander wedges are radially mounted upon said spindle, there being an expander wedge between adjacent expander jaws.

In the embodiment of the invention illustrated, six expander jaws 17 and an identical number of expander wedges and wedge guides are disclosed; however, a greater or lesser number can be utilized with equal facility, it being understood that the greater the number of jaws, the smaller the gap or span therebetween.

Each longitudinally disposed expander jaw 17 is preferably of substantially triangular cross-sectional configuration, including an arcuate outer wall surface 17a and angularly disposed converging inner wall surfaces 17b with a flattened base therebetween. The curvature or radius of the outer wall surface should be lesser than the minimum interior diameter of the plastic pipe to be worked upon whereby the expanding mandrel, when in retracted position, may be received readily within such plastic pipe. Desirably the outer arcuate surface of each expander jaw is stepped down from its inner end to its outer end, as shown at 17d, to assist in the insertion of the mandrel within a pipe extremity.

Each expander wedge 18 includes an arcuate outer longitudinal surface 18a, having a curvature complementary to that of the expander jaws, angularly disposed and diverging side walls 18b, the angular relationship thereof being complementary to that of the converging inner wall surfaces of the expander jaws, and a flattened base portion 180. Each expander wedge 18 is provided with a T-shaped longitudinally disposed and centrally located slot or keyway 18d which extends the full length thereof and within which the complementary T- shaped head 19a of a wedge guide 19 is received, the association being such that the wedge guides 19 may reciprocate freely within the slots 16a in the spindle 16 as the expanding mandrel is adjusted from retracted to expanded position and vice versa.

As shown more particularly in FIG. of the drawings, each expander wedge guide 19 is provided with a T-shaped head portion 19a and a tapered bottom edge 19b whereby the height of each wedge guide decreases from the inner to the outer end thereof, the rate of decrease being complementary to the taper of the spindle 16. Thus, when a wedge guide 19 is received with a slot 160, the outer surface of the wedge guide, and the expander wedge supported thereupon, will at all times lie in a plane parallel to the longitudinal axis of the spindle.

With the spindle, wedge guides, expander wedges, and expander jaws in assembled relationship as described hereabove, suitable means is provided for maintaining the assembly against inadvertent separation, and a preferred form of such means includes an inner flanged end cap mounted in fixed spaced relationship with respect to the standard 12 and an outer flanged end cap 21, which is mounted upon and movable with the reduced outer extremity of the expander 16, as shown more particularly in FIG. 2 of the drawings, the expander jaws 17 and expander wedges 18 being ofa length to fit snugly therebetween.

Desirably, the peripheral surfaces of the expander jaws, wedges and wedge guides are circumferentially notched or recessed adjacent each extremity for the reception of a continuous coil spring or the like 22 whereby the several elements are urged inwardly toward each other and the spindle upon which these components are supported.

As shown more particularly in FIG. 1 of the drawings, the mandrel assembly is mounted in fixed relationship with respect to the mounting plate 11, suitable securing means, such as bolts or the like 23, having one end attached to the inner end cap 20 as shown at 23a and the other end secured to the mounting plate 11 as shown at 23b being provided. It will be noted that the spacing between the expanding mandrel and the mounting plate 11 must be sufficiently great to receive that portion of the spindle which passes through the mandrel when the limit of expansion or enlargement will be approached.

To provide a more certain assembly between the expander wedges and wedge guides and the inner end cap 20, each wedge guide 19 terminates at its inner extremity in a vertically disposed T-shaped head portion 19c and the adjacent face or wall of the end cap 20 is provided with a plurality of radially spaced and complementary T-shaped slots 20a within which the head portions 190 of the wedge guides are received.

To provide a continuous and smooth peripheral surface for the expander jaws 17 which will be spread apart and thus have an increasing gap between adjacent jaws as the operative diameter of the mandrel is enlarged, a stainless steel spring sheath 24 is provided. This sheath, which will have a longitudinal dimension in accordance with the width of enlarged pipe extremity desired, viewed transversely, is spiral with welloverlapping edges and under continual inherent spring tension to urge the expander jaws into firm engagement with the expander wedges. As the diameter of the mandrel is enlarged, theoverlapping edges of the sheath will skip over each other to permit simultaneous enlargement of the sheath. In like manner, as the mandrel diameter is decreased, inherent spring tension or resiliency insures simultaneous reduction in sheath diameter.

This sheath, which is produced from particularly thin sheet material, bridges the gap between adjacent expander jaws and insures uniform enlargement of the extremity of the plastic pipe or tubing and, if desired, the floating end or both edges 24a of the sheath may be feathered or tapered to a knife edge to eliminate any line on the interior surface of the enlarged pipe extremity.

The method of operation of the apparatus discussed in detail hereabove is particularly simple and the steps required in connection therewith are detailed as follows.

It is necessary that the plastic pipe extremity to be enlarged be preheated to facilitate the expansion or enlargement thereof and a suitable heating chamber (not shown) is provided for such purposes. Such units are well-known in this and related arts and are available on the open market as closedloop circulating air blowers with electrical finned heating elements. Temperature elevation on the order of from 250 to 400 F. is adequate for present purposes. Temperatures on the order of 500 F. or higher may blister the plastic pipe and are to be avoided. It has been found in practice that with the heating chamber temperature controlled at 400 F. approximately 1 minute and 20 seconds is required to preheat an 8-inch diameter plastic sewer pipe to a temperature on the order of 250 F, this constituting a soft bell forming" condition.

The preheated plastic pipe extremity 25 is then placed upon the collapsed mandrel, as shown in FIG. 5 of the drawings. The spindle 16 is then moved toward the mounting plate 11, by means of rotation of the handwheel 14, thereby moving the wedge guides 19 outwardly as the upwardly inclined slot or cam tracks 16a slide beneath the bottom edges of said wedge guides. This results in the increase in diameter of the expanding mandrel and encompassing spring sheath, preferably produced from stainless steel with a highly polished exterior surface, with the resultant enlargement of the interior diameter of the plastic pipe to create the belled portion 25a. The expanded pipe extremity is then permitted to cool, the mandrel is closed by moving the spindle in a direction toward the interior of the pipe length and the expanded or belled pipe length, or sleeve, is slipped off or removed from the mandrel.

The degree of enlargement is readily controllable as by a gauge or other indicating media or stop means (not shown) on the apparatus and, in each instance, should be complementary to the exterior diameter of the pipe length to be received therein.

It has been found in practice that a thin sheath or sheet of stainless steel surrounding or encompassing the mandrel or enlarging die adequately bridges any unsupported sections or gaps between the expander jaws. The highly polished surface of this sheath forces the plastic material to slide or flow uniformly with respect to the specific locations of the expander jaws and produces equal enlargement or stretch around the entire surface of the belled extremity resulting in uniform interior and exterior surfaces of the belled portion without substantial gauge variation.

There has been described novel apparatus and method for the enlargement of an extremity of a length of plastic pipe which may be utilized with particular convenience and economy and which includes a novel expanding mandrel having wide-spread utility in the industrial arts.

It will be obvious to those skilled in this art that various changes may be made in the invention without departing from the spirit and scope thereof and reference therefore is had to the claims for summaries of the essentials of the invention and of the novel features of construction and novel combinations of parts, and method of operation, for all of which protection is desired.

What is claimed is:

1. An expanding mandrel assembly comprising, in combination, a plurality of radially disposed expander jaws and a plurality of expander wedges, said expander wedges being located alternately with respect to said expander jaws, each of said expander jaws including an arcuate outer wall surface and angularly disposed converging inner wall surfaces and each of said expander wedges including an arcuate outer wall surface having a radius complementary to that of the expander jaws and angularly disposed diverging side walls having an angular relationship complementary to that of the converging inner surfaces of the expander jaws;

a radially disposed wedge guide associated with each expander wedge, the base of each expander wedge being provided with a longitudinally disposed T-shaped slot for the reception of the complementarily conformed upper extremity of the associated wedge guide;

each of said expander jaws and expander wedges being provided with a circumferential notch adjacent at least one extremity thereof and a continuous coil spring received within said aligned circumferential notches to bias said expander jaws and wedges toward each other;

cam means located axially of said mandrel assembly and movable laterally to increase selectively the diameter of said mandrel, said cam means being constituted by a tapered spindle and each wedge guide having a complementarily tapered inner surface which engages said spindle, the peripheral surface of said spindle being provided with a plurality of longitudinally disposed and uniformly spaced wedge guide receiving slots within which the lower extremities of said wedge guides are slidably received; expansible spring means surrounding said mandrel assembly, said spring means being operative to urge said expander jaws and expander wedges inwardly toward a retracted position; and

inner and outer flanged end caps for said mandrel and spindle assembly, said inner end cap including a vertically disposed wall having a centrally located aperture to permit ready passage therethrough of the axially located cam means, said outer end cap being mounted upon the outer extremity of said cam means and engaging with the outer extremity of said mandrel assembly in surrounding relationship when said cam means approaches the limit of its movement in the expanding direction.

2. An expanding mandrel as set forth in claim 1 where the vertically disposed wall of the inner end cap is provided with a plurality of radially spaced T-shaped slots and the inner extremity of each wedge guide has a complementarily shaped vertical extremity receivable within an associated slot whereby said wedge guides are secured to said inner end cap.

3. Apparatus for enlarging an extremity of a length of a plastic pipe so that the extremity of an adjacent length of plastic pipe may be received and retained therein, said apparatus including a mounting plate, a bracket including an internally threaded handwheel mounted on one face of said mounting plate, and a horizontally disposed threaded adjusting rod extending through said bracket and mounting plate;

an expanding mandrel assembly comprising, in combination, a plurality of radially disposed expander jaws and a plurality of expander wedges, said expander wedges being located alternately with respect to said expander jaws, each of said expander jaws including an arcuate outer wall surface and angularly disposed converging inner wall surfaces and each of said expander wedges including an arcuate outer wall surface having a radius complementary to that of the expander jaws and angularly disposed diverging side walls having an angular relationship complementary to that of the converging inner surfaces of the expander jaws;

a radially disposed wedge guide associated with each expander wedge, the base of each expander wedge being provided with a longitudinally disposed T-shaped slot for the reception of the complementarily conformed upper extremity of the associated wedge guide;

each of said expander jaws and expander wedges being provided with a circumferential notch adjacent at least one extremity thereof and a continuous coil spring received within said aligned circumferential notches to bias said expander jaws and wedges toward each other;

cam means located axially of said mandrel assembly and movable laterally to increase selectively the diameter of said mandrel said cam means being constituted by a tapered spindle mounted upon the inner extremity of said threaded adjusting rod and each wedge guide having a complementarily tapered inner surface which engages said spindle, the peripheral surface of said spindle being provided with a plurality of longitudinally disposed and uniformly spaced wedge guide receiving slots within which the lower extremities of said wedge guides are slidably received; expansible spring means surrounding said mandrel assembly, said spring means being operative to urge said expander jaws and expander wedges inwardly toward a retracted position; and

inner and outer flanged end caps for said mandrel and spindle assembly, said inner end cap including a vertically disposed wall having a centrally located aperture to permit ready passage therethrough of the axially located cam means, said outer end cap being mounted upon the outer extremity of said cam means and engaging with the outer extremity of said mandrel assembly in surrounding relationship when said cam means approaches the limit of its movement in the expanding direction.

4. Apparatus as set forth in claim 3 where said adjustable mandrel includes an inner flanged end cap having a centrally located aperture through which the spindle extends, means being provided to secure said inner flanged end cap to said mounting plate in spaced relation with respect thereto the spacing between said mounting plate and inner end cap being sufficiently great to receive that portion of the spindle which passes through the mandrel when the limit of enlargement will be reached.

5. An expanding mandrel as set forth in claim 1 where the expansible spring means surrounding said mandrel assembly is a stainless steel spring sheath having overlapping edges and adjustable with said mandrel to provide a smooth peripheral surface for at least a portion of the length of said expander aws.

6. Apparatus for enlarging an extremity of a length of plastic pipe as set forth in claim 3 where the expansible spring means surrounding said mandrel assembly is a stainless steel spring sheath having overlapping edges and adjustable with said mandrel to provide a smooth peripheral surface for at least a portion of the length of said expander jaws. 

1. An expanding mandrel assembly comprising, in combination, a plurality of radially disposed expander jaws and a plurality of expander wedges, said expander wedges being located alternately with respect to said expander jaws, each of said expander jaws including an arcuate outer wall surface and angularly disposed converging inner wall surfaces and each of said expander wedges including an arcuate outer wall surface having a radius complementary to that of the expander jaws and angularly disposed diverging side walls having an angular relationship complementary to that of the converging inner surfaces of the expander jaws; a radially disposed wedge guide associated with each expander wedge, the base of each expander wedge being provided with a longitudinally disposed T-shaped slot for the reception of the complementarily conformed upper extremity of the associated wedge guide; each of said expander jaws and expander wedges being provided with a circumferential notch adjacent at least one extremity thereof and a continuous coil spring received within said aligned circumferential notches to bias said expander jaws and wedges toward each other; cam means located axially of said mandrel assembly and movable laterally to increase selectively the diameter of said mandrel, said cam means being constituted by a tapered spindle and each wedge guide having a complementarily tapered inner surface which engages said spindle, the peripheral surface of said spindle being provided with a plurality of longitudinally disposed and uniformly spaced wedge guide receiving slots within which the lower extremities of said wedge guides are slidably received; expansible spring means surrounding said mandrel assembly, said spring means being operative to urge said expander jaws and expander wedges inwardly toward a retracted position; and inner and outer flanged end caps for said mandrel and spindle assembly, said inner end cap including a vertically disposed wall having a centrally located aperture to permit ready passage therethrough of the axially located cam means, said outer end cap being mounted upon the outer extremity of said cam means and engaging with the oUter extremity of said mandrel assembly in surrounding relationship when said cam means approaches the limit of its movement in the expanding direction.
 2. An expanding mandrel as set forth in claim 1 where the vertically disposed wall of the inner end cap is provided with a plurality of radially spaced T-shaped slots and the inner extremity of each wedge guide has a complementarily shaped vertical extremity receivable within an associated slot whereby said wedge guides are secured to said inner end cap.
 3. Apparatus for enlarging an extremity of a length of a plastic pipe so that the extremity of an adjacent length of plastic pipe may be received and retained therein, said apparatus including a mounting plate, a bracket including an internally threaded handwheel mounted on one face of said mounting plate, and a horizontally disposed threaded adjusting rod extending through said bracket and mounting plate; an expanding mandrel assembly comprising, in combination, a plurality of radially disposed expander jaws and a plurality of expander wedges, said expander wedges being located alternately with respect to said expander jaws, each of said expander jaws including an arcuate outer wall surface and angularly disposed converging inner wall surfaces and each of said expander wedges including an arcuate outer wall surface having a radius complementary to that of the expander jaws and angularly disposed diverging side walls having an angular relationship complementary to that of the converging inner surfaces of the expander jaws; a radially disposed wedge guide associated with each expander wedge, the base of each expander wedge being provided with a longitudinally disposed T-shaped slot for the reception of the complementarily conformed upper extremity of the associated wedge guide; each of said expander jaws and expander wedges being provided with a circumferential notch adjacent at least one extremity thereof and a continuous coil spring received within said aligned circumferential notches to bias said expander jaws and wedges toward each other; cam means located axially of said mandrel assembly and movable laterally to increase selectively the diameter of said mandrel, said cam means being constituted by a tapered spindle mounted upon the inner extremity of said threaded adjusting rod and each wedge guide having a complementarily tapered inner surface which engages said spindle, the peripheral surface of said spindle being provided with a plurality of longitudinally disposed and uniformly spaced wedge guide receiving slots within which the lower extremities of said wedge guides are slidably received; expansible spring means surrounding said mandrel assembly, said spring means being operative to urge said expander jaws and expander wedges inwardly toward a retracted position; and inner and outer flanged end caps for said mandrel and spindle assembly, said inner end cap including a vertically disposed wall having a centrally located aperture to permit ready passage therethrough of the axially located cam means, said outer end cap being mounted upon the outer extremity of said cam means and engaging with the outer extremity of said mandrel assembly in surrounding relationship when said cam means approaches the limit of its movement in the expanding direction.
 4. Apparatus as set forth in claim 3 where said adjustable mandrel includes an inner flanged end cap having a centrally located aperture through which the spindle extends, means being provided to secure said inner flanged end cap to said mounting plate in spaced relation with respect thereto the spacing between said mounting plate and inner end cap being sufficiently great to receive that portion of the spindle which passes through the mandrel when the limit of enlargement will be reached.
 5. An expanding mandrel as set forth in claim 1 where the expansible spring means surrounding said mandrel assembly is a stainless steel spring sheath having overlapping edges and adjustable With said mandrel to provide a smooth peripheral surface for at least a portion of the length of said expander jaws.
 6. Apparatus for enlarging an extremity of a length of plastic pipe as set forth in claim 3 where the expansible spring means surrounding said mandrel assembly is a stainless steel spring sheath having overlapping edges and adjustable with said mandrel to provide a smooth peripheral surface for at least a portion of the length of said expander jaws. 